Noise in digital photography can be caused by high ISO settings, long exposure times, poor lighting conditions, or a combination of these factors.

Gaussian noise is the most common type of noise in digital photography. It is characterized by a bell-shaped distribution of pixel values.

Noise reduction removes noise from an image, while sharpening enhances the edges of objects. Noise reduction is a post-processing technique, while sharpening can be done both in-camera and as a post-processing technique.

The two main types of noise reduction techniques are spatial noise reduction and frequency noise reduction.

Spatial noise reduction operates on individual pixels, while frequency noise reduction operates on groups of pixels. Spatial noise reduction reduces noise in the spatial domain, while frequency noise reduction reduces noise in the frequency domain. Spatial noise reduction is more effective at removing high-frequency noise, while frequency noise reduction is more effective at removing low-frequency noise.

Common spatial noise reduction techniques include the median filter, bilateral filter, and non-local means filter.

Common frequency noise reduction techniques include the Wiener filter, wavelet transform, and Fourier transform.

The median filter is best for removing high-frequency noise.

The Wiener filter is best for removing low-frequency noise.

Noise reduction can reduce the sharpness of an image, introduce artifacts into an image, and increase the processing time of an image.

You can minimize the drawbacks of noise reduction by using a noise reduction technique that is appropriate for the type of noise in your image, applying noise reduction sparingly, and using a high-quality noise reduction software.

Some of the best noise reduction software programs include Adobe Photoshop, Adobe Lightroom, DxO PhotoLab, and Noise Ninja.

Some of the best practices for noise reduction in post-processing include shooting in RAW format, using a low ISO setting, using a fast shutter speed, and using a tripod.

The most important thing to remember when using noise reduction is that it is not a cure-all. Noise reduction can be used to improve the quality of an image, but it can also be used to remove noise from an image.